Aircraft landing gears comprising a steered lower part and a steering device designed to turn the steered lower part in response to a steering command are known. Conventionally, such a landing gear comprises a strut assembly, an orientable strut sliding in the strut assembly and bearing the wheels, a steering tube mounted with the ability to rotate and a torque link connecting the steering tube and the orientable strut in terms of rotation. The steering device acts on the steering tube to make the orientable strut turn and therefore also the wheels via the torque link.
There are numerous types of steering device: some comprise one or two hydraulic jacks, others a rack-type actuator, others still, an electromechanical actuator, etc.
Thus, in the field of naval aircraft carried on carriers, it is known practice to use a steering device comprising an actuator with a hydraulic motor collaborating with a toothed wheel secured to the steered lower part of the landing gear.
In the field of light aircraft, it is known practice to use a steering device comprising an actuator with an electric motor collaborating with a toothed wheel secured to the steering lower part of the landing gear.
Within the context of the development of a more electric aircraft, numerous studies are looking to improve the existing steering devices equipped with an electromechanical actuator.
Such a steering device is equipped with damping means intended to limit the transmission of vibration from the wheel to the rest of the landing gear when the aircraft is on the ground. This vibration is caused notably by the “shimmy” which in general refers to a phenomenon of torsional oscillation of vertical axis likely to arise on a landing gear when the aircraft is running along the ground at a sufficiently high speed. This vibration is also the result of the release of energy at the moment of a blow-out of a tyre of a wheel of the landing gear on landing.
In order to limit the load supplied to the actuator and the landing gear, it has been envisioned for a torque limiter to be introduced into the electromechanical actuator drive train, the role of this torque limiter being to protect the electromechanical actuator and the structural components of the landing gear and to absorb and dissipate the energy released in a tyre blow-out.
Because the torque limiter is incorporated directly into the drive train, its use makes it impossible to disconnect the output shaft of the motor from the steering tube, because such disengagement would lead to deactivation of the damping means. Thus, in order to tow the aircraft around on the runway, use is made of the reversibility of the drivetrain of the electromechanical actuator, and this imposes great constraints on the design thereof. This solution has no means of damping the oscillations caused by the shimmy and generating loads below the torque limiter actuation threshold.